Art of heat transfer



2 Sheets-Sheet l 0/15 OUTLET ART OF HEAT TRANSFER Filed Sept. 22. 1931jfiJNVENTOKS By "7 W v Mn A TTORNEYS.

7.9. d V'- s" W W. 5. PATTERSON ET AL Dec. 26, 1933.

Dec. 26, 1933. w. s. PATTERSON ET AL 1,941,365

ART OF HEAT TRANSFER Filed Sept. 22. 1931 2 Sheets-Sheet 2 G I70 I301216 k HA Te; m M

IN V EN TORS W /mm?- V A TTORNEYS.

UNITED STATES PATENT OFFICE ART or HEAT TRANSFER Ward S. Patterson,Cranford, N. J., and 'Fay Harry Rosencrants, Scarsdale, N. Y., assignorsto International Combustion Engineering Corporation, New York, N. Y., acorporation of Delaware I Application September 22, 1931 Serial No.564,298

22.0laims. (Cl. 257-245) This invention relates to the art of heattransof heating surface in the heater, depending upon fer, andparticularly to certain novel and adthe variation in operating rate.This, of course, vantageous methods and apparatus for transferinvolvescomplications in the heat exchanger, or, ring heat from flue or furnacegases to air which as an alternative, the expensive necessity of is tobe preheated for admission into a furnace maintaining a plurality ofexchangers of differfor us i n pu p s s. ent capacity, one or more ofwhich must stand The invention primarily contemplates the idle whileanother is in use. Our invention, transfer of heat from furnace gases toa combroadly considered, involves the obviation of the bustion airstream, whereby the temperature of various -difliculties above outlined,by the cm- D the discharged gases is lowered and the temployment ofcertain novel methods and forms 6 perature of the air raised, foreconomical power of apparatus for regulating or controlling thep a p asp ial y by an i pr ved oounfluid flow to accomplish the desired ends. eflOW d, in Such manner that While a high More specifically, thepreferred operation acd ee of efl y s Obtained. y the p cording to thepresent invention involves the ature of h flue a es j n h dischargecontrolling of the flow of the heating fluid, as

Point thereof from the Z0116 of heat transfer is having certaindesirable advantages over the conmaintained at such a level, regardlessof the rate t l of th h ted fluid of operation of the furnace orfurnaces, that As 111 appear in more d t il hereinafter, substantialcondensation of condensibles carried several methods are cof templated,d v r l by the gases, and consequent clogging as Well forms of apparatushave been devised, all inas corrosion of the heat transfer mechanism orvowing basically certain general advantages, but apparatus arePreventedeach involving specifically certain advantages of For a clearunderstanding of the invention its w V and of the advantages thereof itshould here be one method f carrying out the invention stated that inthe preheating of air for boiler valves the by passing of least aportion of 80 furnaces or other furnaces, where the furnace or thestream, and th method involves flue-gases are used as the heating mediumsoot the recirculating of a part of the air stream in and dust and gummydeposits are aptto be lodged a certain manner; at the cold or gas outletend of the air Other, and more preferred methods, involve heater,especially when the boiler is operating at the diversion of a portion ofthe gas stream in 85 10w loads' It is further quite dimcult variousnovel ways, the recirculation of a porvide means for cleaning frequentlyand wlthout tion of the gas stream, or the dilution of at leastshutdown,the heat transfer plates or elements a portion of the stream by at leasta portion of the heater and the installation of nozzle 9 of the gasstream. These various features and jet devices for blowing the soot andother deposit advantages of the invention will be more fully 90 out ofthe heater from title gas exit end thereof appreciated from thefollowing description, taken is disadvantageous, particularly because ofthe together with the accompanying drawings in necessity of blowingagainst tttllie l cllirezction ofthe which u gas stream passing throughe ea er. e

40 I In heat exchangers of the counterflowtype, gg f g zfig g g gz gfigg g f gl 95 which are desirablefor their general efllciency, heater wone form ,of our invention applied and especially at times when aboilerdfumace 1S thereto operating v atlow loads, clogging an corrosionecfi th line frequently take, lace adjacent the air inlet end jg $;rg gfl of 1 of the heater where the cold air on one side of I I c t,

h lateorl ates and comparatively cool gas ti re Q QBF a; V .En the otherg idejthereof result causing'the --,l.1gure 2a is a. seicfitioltif sumlg kfiq a g'z gf fi temperatureiof tne'gas m adjacent the plate s at a md 9% on0 t; v or plates. to fallb low the 'dew-p'oin This'de- F re irmen rr i an me ieee n pends, oi coursefongthef two fluid temperatures,vatitonal wew anfl her m difieation pf the in- 105 cleanness or thesurface, and the composi- V .1; r p 3:31 of the 'flue gas,especially-with reference to .Figure 3,,1 s a;,diagrammat cview of amodules; its contentofwater vapors and sulphuntrioxide. ton'bfthwmvention, showing a heat exchanger We are aware that it hasbeen'proposedto mini- '01 am heaterm =1t relation to the gas a k mizethis difficulty by using a variable amount ducts and the induced draftand forced draft no a power plant or 'boiler furviews of still othermodifications.

By reference first to- Figures 1 and 2, it will be seen that we haveillustrated an air preheater which includes a conduit-like casing 2,having a fluid or gas inlet 3, a fluid or gas outlet 4, a fiuid or airinlet 5, and a fiuid or air outlet 6.

In accordance with known practice, groups of heat transfer elements orpartition walls '7-'l--7 are disposed in 'the casing 2, extendinglengthwise thereof, the air inlet and outlet communicating withalternate passageways 8 formed by the walls '7, and the gas inlet andoutlet communicating with the alternate intermediatepassages 9. Spacerstrips or angle members 10 are provided in the gas and air passagewaysto position the plates 7 and to insure the proper distribution of gasand air over the entire heat transmitting surface or area. The spacerstrips 10 shown in Figure 1 are strips in the gas passageways, which, inaccordance with the usual practice, are broken away at zones indicatedat 1111, to permit of inspection and lancing when necessary, through theapertures or doorways covered by the doors 12. i

'While we have preferred to illustrate a heat exchanger of the so-calledplate type, it is to be understood that the invention may be equallywell applied to heat exchangers of the so-called tubulartype.

In accordance with the present invention, we provide a diverting orby-pass passageway or channel 13, leading from the gas inlet 3 to 'anadvance point or zone in the gas passageways of the heater proper, wherethe said by-pass communicates, at the area indicated by the numeral 14with the said gas passageways; break away the spacer elements 10 at thepoints marked 15 and 16, in the gas passageways, which provides, in eachgas passageway, a substantially triangular zone adjacent the gas outletand air inlet end of the heater, as clearly shown in Figure 1; andprovide control means for the gas by-pass,- such as the movable damper17, which may be manually controlled by means of its shaft 18, or whichmay be controlled by a thermostat 18a of any desired type locatedpreferably adjacent the gas outlet 4.

In Figure 2 the gas by-pass 13 is formed by angle members 10a which areattached to plates 7, the flanges 10b of the angle members being inalinement to form the inside wall of the by-pass. Thus a very simplearrangement is provided whereby a heater may be manufactured with theby-pass arrangement applied at practically the same cost as a heater notequipped with the improvement. In some instances, however, it-may bedesirable to form the gas by-pass 13 by employing a casing plate 'orwall 10c as illustrated in Figure 2a.

According to the construction just described, hot flue gas at thetemperature available as it enters the heater is diverted or by-passeddirectly to the area or zone adjacent the gas exit end of the heaterthereby increasing the heat transferred to the air immediately as thelatter enters the heater, and'thereby raising the plate temperature ofthis area near the air inlet. It is obvious that the changes necessaryin the ordinary heater to carry out this invention are very easilyaccomplished. The gas by-pass may be entirely self-contained within theair heater casing and the fiow of gas through the by-pass may easily bethermostatically controlled by means of the damper 1'7. The use of theinspection, access or lancing openings above referred to, for handlancing, is not interfered with in any way.

Referring, now, to Figure 3, we have diagrammatically illustrated an airpreheater 2a, the fiue gas side of which is indicated at 2b, and the airside of which is indicated at 20, the forced draft fan for the furnacebeing indicated at FD, and the induced draft fan for the furnace beingindicated at ID. The reference character G indicates the fiue gas lineor conduit, the reference characters CA indicate the cold air line, andthe reference characters HA indicate the hot air line to the furnace. Inthis formof construction, as in the form shown in Figures 1 and 2, aportion of the gas is by-passed through the by-pass 13a, into the heaterat point 14a, controlled by the valve device indicated at 17a, but wehave also provided an additional valve 19 in the 'gas line, between thepoint of takeoff of the by-pass 13a and the main point of entry of thegas into the heater. By proper manipulation of the 1 valves 17a and 19,both of which may be controlled by a single thermostat adjacent the gasoutlet, any desired portion or all of the gas may be passed through theby-pass or through the gas passages 2b. The advantage of this arrange- 1ment over that shown in Figures 1 and 2 chiefly resides in the fact thatpositive control, as to any proportion, is assured, without having todepend upon pressure differences due to the resistance of the gaspassages in the heater. 1

Reverting now to Figure 1, it will be seen that in addition to thedamper means 17 above described, we also contemplate the provision ofdampers 3a mounted on shafts 3b, by means of which the gas quantitypassing through the by- 1 passducts 13 may be controlled withoutdepending entirely on the difference in resistance to flow between thepassages through the preheater and the bypass ductsu Thus an arrangementis provided the operation of which is positive and fiex- 1 ible andsimilar to that of the form illustrated in Figure 3. In some instances,however, the form illustrated in Figure 1 may be advantageously employedwithout the dampers 3a.

In Figure 4, we illustrate a construction in which a passage 20communicates between the discharge line of the fiue gas fan and theintake line of the combustion air fan, so that a mixture of hot gas andcold air, indicated at WA, is delivered into the fan FD and thus to theheater. Suitable valves 21 in the gas line and 22 in the diluting lineafford control of the system. This arrangement is advantageous ininstallations where a certain proportion of flue gas in the combustionair, especially at low rates of operation of the boiler furnace, will dono harm, or is desired. Admission of fiue gas into the preheated air issometimes desirable for controlling combustion in the furnace.

In the modification shown in Figure 5, somewhat similar parts areemployed, but the air diluting passage 20a in this instance leadsv fromthe hot or inletend of the gas line, and itscontrol is effected by anauxiliary blower AB. The principal advantages of this arrangement overthe arrangement shown in Figure 4 are: That the positive delivery of theflue gas into the forced draft blower or fan is controllable quiteindependently of the action of the induced draft fan ID, and that thegas delivered through the conduit 1 20a into the air line need beonly'about 10% of the quantity of air handled as compared with about 25%of the quantity of air handled in the construction shown in Figure 4.This comparison assumes a temperature of gas entering the heater ofapproximately 600 F. and a gas leaving temperature of about 300 F. Avalve 20b is provided in the line 20a, preferably at a point near theline G, for controlling the fan delivery and preventing air infiltrationbackward when the fan is not operating.

In the construction shown in Figure 6, any desired proportion of theexit gases may be recirculated or redelivered, by the diverting line 23,back to the gas inlet line. By the provision of a valve 24 in line 23and a valve 25 in the line leading from the induced draft fan ID tothestack, any desirable recirculation pressure is available, even at themost reduced furnace loads, at which times it is generally mostnecessary to effect the recirculation.

While the invention contemplates, if desired, the by-passing of acertain amount of the cold air, for example, directly from blower FD inFigure 3 to line HA; or a recirculation of hot air from line-HA into theintake side of blower FD, we prefer to control, divert or vary the flowof the gas or heating medium, since this causes little or nointerference with the desired, independentcontrol of the air feed to theboiler furnace.

In the modification illustrated in Figure 2b, we have shown a novelarrangement of additional and easily replaceable heat absorbing surfaceover which the by-pass portion of the hot gas may be passed to effectinitial preheating of the air before it enters the heater proper.

This surface may consist of readily replaceable heater elements ofeither the tubularor plate type, although we prefer to employ tubularelements with extended surface on the gas or air side. Through thisarrangement the air may be positively preheated to a pre-determined andcontrollable temperature before it enters the main part of the heatexchanger. Dampers such as the dampers 3a and 17 described in connectionwith the form illustrated in Figure 1 may be employed to control theflow of the gas, making it possible to vary the amount of gas bypassedto suit the requirements which will depend on the ambient airtemperature, the gas temperature leaving the heater, the amount ofcondensibles in the gas, and the amount of solid foreign matter in thegas which tends to cause clogging when such matter is moistened due tothe condensation of the condensibles.

In any of ire arrangements, the valves or blowers will be so adjusted,or the thermostat or thermostats contriolling them will be so set thatthe relative flow of the heated and heating media will be suitablycontrolled or varied to prevent the exit gases from falling intemperature below the dew-point of condensibles carried thereby. It willbe readily seen that the controlling of .the problem involved, incounter-flow heat exchanging, by suitably varying the gas flow, hasdecided advantages over prior practices involving the employment ofcomplicated apparatus or a plurality of heat exchangers for vary-' ingthe heat-transfer surface.

While we have referred .to the device as an air preheater and to itsapplication to a' boiler furnace or other furnace, it is to beunderstood that we contemplate its use as a heat exchanger receiving hotgas from any source and utilizing it to heat air or other gaseous fluidssuch as gaseous fuel, or for use in connection with various types offurnaces, or in connection wit various other processes or apparatus. I

What we claim is:

1. The improved method of transferring heat between two flowing gasstreams which includes counterfiowing the streams in generally separatedbut heat-transferrent proximity through a given zone whereby the coldestportion of the stream to be heated is adjacent the coolest portion ofthe heating stream, and controlling the flow of at least a part of theheating stream in such manner as to maintain the coolest portion of theheating stream in said zone above the dew-point of condensibles carriedthereby without affecting the entering state of the gas stream to beheated.

2. The improved method of transferring heat between two flowing gasstreams which includes counterflowing the streams in generally separatedbut he'at-transferrent proximity through a given zone whereby thecoolest portion of the stream to be heated is adjacentthe coolestportion of the heating stream, and diverting the flow of at least a partof the heating'stream in such manner as to maintain the coolest portionof. the heating stream in said zone above the dew-point of condensiblescarried thereby without affecting the entering state of the gas streamto be heated.

3. The improved method of transferring heat from a stream of hot furnacegases to a stream of air for combustion which includes counterfiowingthe streams in generally separated but heat-transferren't proximitythrough a given zone whereby the coldest portion of the air stream isadjacent the coolest portion of the gas stream, and controlling the flowof at least a part of the gas stream in such manner as to maintain thecoolest portion of the gas stream in said zone above the dew-point ofcondensibles carried thereby without affecting the entering state of thestream of air for combustion.

4. The improved method of transferring heat from a stream of hot furnacegases to a stream of air for combustion which includes counterfiowingthe streams in generally separated but heat-transferrent proximitythrough a given zone whereby the coldest portion of the air stream isadjacent the coolest portion of the gas stream, and bypassing the flowof at least a part of the gas stream in such manner as to maintain thecoolest portion of the gas stream in said zone above the dew-point ofcondensibles carried thereby without affecting the entering state of thestream of air for combustion.

5. The improved method of transferring heat from a stream of hotfurnacegases to a stream of air for combustion which includes counterfiowingthe streams in generally separated but heat-transferrent proximitythrough a given zone whereby the coldest portion of the air stream isadjacent the coolest portion of the gas stream, and recirculating theflow of at least a part of the gas stream in such manner as tomaintainthe coolest portion of the gas stream in said zone above thedew-point of condensibles carried thereby without affecting the enteringstate of the stream of air for combustion.

6. In a heat exchanger, associated passageways respectively for hot gasand gas to be heated, inlet and outlet means for the respective gaspassageways, and controllable supplemental gas passage means for the hotgas adapted to vary its normal flow for controlling he temperature gasto be heated.

7. In a heat exchanger, associated passageways respectively for hot gasand gas to be heated, in-

let and outlet means for the respective gas passageways, andcontrollable supplemental gas passage means for the hot gas adapted tovary its normal flow for maintaining the temperature of the passagewaywalls adjacent the hot gas outlet in a range above the dew-point ofcondensibles carried in thegas without afiecting the entering state ofthe gas to be heated.

8. In a heat exchanger, associated main passageways respectively for hotgas and gas to be heated, inlet and outlet means for the respective gaspassageways, and means for controlling the temperature of the passagewaywalls adjacent the hot gas outlet comprising a controllable by-passfor-by-passing hot gas from the main hot gas passageway adjacent its inletand for returning it thereto adjacent its outlet.

9. In a heat exchanger, associated main pas-' passageways, and means forcontrolling the tem-- perature of the passageway walls adjacent the hotgas outlet comprising means for by-passinghot gas into the exit zone ofthe hot gas passages.

11. In a heat exchanger, associated-passageways respectively for hot gasand gas to be heated, inlet and outlet meansfior the respective gaspassageways, and means for controlling the temperature of the passagewaywalls adjacent the hot gas outlet comprising means for controllablyre-circulating through the hot gas passages a portionpfthe heating gas.

' 12. In an air-preheater apparatus, a flue-gas line, a combustion-airline, a counterflow heat exchanger through'which said lines run, meansfor setting up a flowing. stream of fine gasesthrough the gas line,means for setting up a flowing stream of air through the air line, .anda bypass for the flue gas line leading therefrom at the gas entering endportion of the exchanger and returning thereto at the gas exit endportion of the exchanger whereby a portion of the flue gas stream isby-passed to efiect the maintenance of the temperature of the flue gasstream adjacent its exit from the exchanger above a predetermined point.

13. In a heat exchanger, a casing having air and" gas inlets and outletsarranged for counterflow of gas and air through the exchanger, heatexchanging elements in said casing, and a by: pass for by-passing gasfrom the gas inlet to the gas outlet over heat exchanging surface whichis adjacent the air inlet.

14. In a heat exchanger, a casingh'aving air and gas inlets and outletsarranged for counterflow of gas and air through the exchanger, heatexchanging elements in said casing providing pas,- sages for the air andgas, and means providing a passage independent of the heat exchangingunit adapted to be removed as such from the element passages for leadinggas directly from the gas inlet to the gas outlet over heat exchangingsurface which is adjacent the air inlet.

15. In a heat exchanger, a casing having air and gas inlets and outletsarranged for counterfiow of gas and air through the exchanger, heatexchanging elements in said casing, and a by-pass for by-passing gasfrom the gas inlet over heat exchanging surface which is adjacent theair inlet, said by-pass being formed in part by the casing and in partby the heat exchanging elements.

16. In a heat exchanger, a casing having air and gas inlets and outletsarranged for counterllow of gas and air through the exchanger, heatexchanging elements in said casing, and a bypass for by-passing gas fromthe gas inlet over heat exchanging surface which is adjacent the airinlet, said by-pass being formed in part by the casing and in part bymeans carried by the heat exchanging elements.

17. In a heat exchanger, a casing having air and gas inlets andoutlets'arranged' for counterflow of gas and air through the exchanger,main heat exchanging elements in said casing, supplemental heatexchanging elements located in said casing adjacent the air inlet forsubjecting the stream of air to heat as it enters the exchanger, andmeans for diverting gas from the gas inlet to the supplemental heatexchanging elements.

18 In a heat exchanger, a casing having air and gas inlets and outletsarranged for counterflow of gas and air through the exchanger, main heatexchanging elements in said casing, supplemental heat exchangingelements located in said 110 casing adjacent the air inlet, and meansfor diverting gas from the gas inlet to the supplemental heat exchangingelements, said supplemental heat exchanging elements comprising a.

heat exchanger. 1

19. In a heat exchanger of the counterfiow type having the usual heatexchanging elements, the inclusion of supplemental heat exchangingelements located between the point of admission of the gas to be heatedand the usual heat exchanging elements and over which all said gas mustfiow on entering the exchanger.

20. In a heat exchanger of the counterflow type having the usual heatexchanging elements, the inclusion of supplemental heat exchangingelements located between the point of admission of the gas to be heatedand the usual heat exchanging elements and over which all said gas mustflow on entering-the exchanger, and means for leading heating gasdirectly to said supplemental heat exchanging elements.

21. Ina heat exchanger, associated passageways respectively for hot gasand gas to be heated, inlet and outlet means for the respective gaspassageways, and means for controlling the temperature of passagewaywalls comprising means for re-circulating through the hotgaspassageature of passageway walls comprising means for re-circulatinghot gas from its outlet back into its passageway and over passagewaywalls.

WARD S. PATTERSON. FAY HARRY ROSENCRAN'I'S.

